SUMMARY: The overall goals of this project are to define the host cell and virus functions responsible for the regulation expression of viral functions during polyoma virus replication. In particular, the control of the switch-over to the expression of late gene functions following the onset of viral DNA synthesis is under study. A unique new type of polyoma variant (3049) has been described whose phenotype is recognized by the production of capsid proteins at 2-3 fold the rate of that found in a wild-type virus. This increased rate of capsid protein synthesis is correlated directly with the presence of 2 fold more virus-specific, polyadenylated RNA both in the nucleus and on cytoplasmic polyribosomes. This finding has suggested that the phenotype of the variant virus is due to an altered rate of transcription of at least the late genes coding capsid protein. BIBLIOGRAPHIC REFERENCES: Tachovsky, T. G. and Hare, J. D., A polyoma virus strain with enhanced synthesis of capsid protein. J. Virology 16, 116, 1975. Hare, J. D., Distinctive alterations of nucleoside, sugar and amino acid uptake by sulfhydryl reagents in cultured cells. Arch. of Biochem. and Biopsy. 170, 347, 1975.